This invention relates generally to an improved method of recapping tires, and particularly to a method of curing new treads onto old tires for both automobile and truck tires.
In the past, tires have been recapped in pressure kettles under pressurized steam or pressurized hot water. The tire tread is placed over the periphery of the tire to be recapped and then a covering is placed over the tread and tire surface to hold the tread on the tire while the heat from the steam or water cures the tread onto the tire.
Problems have arisen for several reasons, one being that the cover usually would not completely cover the tire and so water and water gas would get in between the tire and tread to interfere with the curing. The covers were then replaced with flexible envelopes which were airtight. However, the problem then became that under the high pressure of about 80 psi needed to cure the tread onto the tire, air bubbles force their way into the tire rubber again resulting in the production of an inferior product.
More recently, vacuum pumps have been used to pump the air out of the envelope before the heat and pressure is applied to avoid the air bubble problem. The addition of a vacuum pump system also results in the addition of extra cost to the system.
Again, another problem using the known systems is that quite often the envelopes would be flawed and the flaw would not be detected until after the water has covered the tires or the steam has been introduced into the kettle. It should be noted that at the present level of technology in the industry, the failure rate of these envelopes is normally in the range of 10%. An earlier system of detecting flaws in the envelopes is therefore necessary to lower costs and increase productivity.
The present invention relates most closely to the "hot water system" of recapping tires. The use of hot water is preferred to the use of steam as with steam curing the temperature is usually quite in excess of that preferred if the desired pressure is to be obtained. As well, when the steam system is used, cold air must first be pumped into the system to get the pressure up before the steam is introduced as the early introduction of steam will result in an unsatisfactory curing at too low a pressure. This means that there is a need for a two-step system, one to first introduce air to raise the pressure and one to then introduce steam to raise the temperature. A hot water system is a single step system as the water supplies both the temperature and pressure and so is much simpler to operate.
In the present invention, the recapped tire is first placed within the envelope which is completely sealed. Then the sealed envelopes are hung in the kettle. Present methods demand that a vacuum line be run from the envelope to a vacuum unit outside the kettle. A vacuum is drawn on each envelope and the envelope is collapsed onto the recap holding it in place during the curing.
The kettle is then shut and water at about 200.degree. F and 80 psi is pumped into the kettle. The recapped tires cure therein for about four hours if they are normal automobile car tires. Of course, the time will vary depending on many factors including the tire size.
When the curing is completed the water is removed from the kettles and the tires from the envelopes. Quite often, the recess in the bottom of the tire is filled with water when the operation is completed. A system is therefore needed which would automatically remove the water from these recesses.
With the types of vacuum units used to collapse the envelope, if the envelope has a leak of any kind it is usually not detected until the water has filled into the kettle to the extent that the flaw is covered with water and water is being drawn into the vacuum pump. The kettle must then be emptied and the flaw located and fixed. A method is therefore needed to help in detecting leaks before the water filling step has proceeded too far.